Learn about the science behind the current exploration of the solar system in this free class. Use principles from physics, chemistry, biology, and geology to understand the latest from Mars, comprehend the outer solar system, ponder planets outside our solar system, and search for habitability in our neighborhood and beyond. This course is generally taught at an advanced level assuming a prior knowledge of undergraduate math and physics, but the majority of the concepts and lectures can be understood without these prerequisites. The quizzes and final exam are designed to make you think critically about the material you have learned rather than to simply make you memorize facts. The class is expected to be challenging but rewarding.

Taught By

Mike Brown

Transcript

We're going to talk about Curiosity's first year of exploration on Mars. The mission was built to explore for ancient inhabitable environments. And here you see Curiosity on the right. And on the left you've got Pathfinder. Which is about the size of a microwave oven. It was built to launch the future of mobile robotic exploration on Mars. It's a little rover with six wheel rocker bogey suspension, which is designed for the rover to drive over rocks about the size of the diameters of the wheels, which relative to the size of the vehicle is actually pretty large. And that suspension system allows the rover, deck to not be tilted very much, which is important, because it's solar powered. That mission analyzed a couple of rocks, drove around a few tens of meters, and then, in 2004, we've got Opportunity that landed on the surface of Mars. And you see the Heritage there. Six wheel rock or bogey suspension, much larger panel of, of solar and that mission was designed to look for evidence of water on the surface of Mars and it was successful. And because it was successful, we then got the green light for Curiosity. Again, you can see the Heritage six wheel rock or bogey suspension. But now this rover consumes so much energy, we had to move to a nuclear power source. So it's got a plutonium 238 source, which decays. And it generates heat, and we capture that heat in a thermal couple, and generate electricity, about 100 watts every hour is what that rover produces. And based on that small amount of energy, we have ten scientific instruments, and 17 cameras that allow us to study the geology and geochemistry. And in addition to that, inside the belly of the rover, we've got an X-ray diffraction unit, which takes powders of rock that we, that we create by drilling, and tells us, quantitatively, what the mineral abundances are. And then we have another instrument called sample analysis of Mars that has something called a quadrupole mass spectrometer, which tells us what the masses of all the elements are that are present. And then in addition to that, it's got a gas chromatograph, that if we see any organic compounds, it can tell us the molecular structure of what those compounds are. And it also has something called a tunable laser spectrometer that allows us to measure the abundance and composition of gases in the atmosphere. Gases that we generate by heating them up inside an oven of, of rock samples. And it also gives us the isotope ratio of important elements like hydrogen, and carbon, and oxygen, and, and we're working on sulfur now. And now let's take a step back in the history of exploration of Mars. And this is old vintage data with Mariner 9 data on the top, and Viking data on the bottom. And at the time, when scientists first looked at this, they imagined that some kind of a fluid was flowing across Mars and caused the rocks to be eroded. And, and there was a debate that lasted for decades about what the composition of this fluid was. And to sort of fast forward, we now feel very confident that the, the fluid that was present was water. Wasn't something like CO2, or liquid nitrogen, or something exotic like that. The important thing is, is that if you're a geomorphologist, you look at these patterns and you think these are the sign of dissection of rocks by flowing water, over solid material. And the flowing fluid exerts a shear stress and it moves particles along that causes abrasion of the bedrock. And so, for decades, that was our view of, the presence of water on Mars, if you look just at, at geomorphic evidence. If, if you ask in places like Nirgal Vallis, where we saw those beautiful drainage networks, where we know that rocks were being eroded. Where we know that sediment was being transported, it took several decades of orbiters to eventually make a big discovery [COUGH] that that material's actually conserved. It doesn't, for example, fly out of orbit and, and, and is lost to space. It comes duressed in a place where the flowing fluid enters a low point, maybe even ponding to form a lake or maybe a small ocean. And there's a divergence in the flux of the water, which decreases the capacity of that water to transport sediment, and it drops out. It does it just like it does on Earth. So you're looking at a delta. I think the most spectacular delta on Mars is called Eberswalde Delta, and, and what you see here is a trunk stream that comes in on the left and then it branches and bifurcates into dozens of tributaries that must have entered a body of standing water. And so, from orbit, we have a really good feeling that there was a lake here. But we just can't prove it until you get on the ground. So that was one of the reasons to send Curiosity to a place on Mars where we believed that there was strong evidence, not just geomorphologically but also spectroscopically in, in terms of minerals that we think have water in their structure. And, and so we pick El Crater, which is real interesting. A big old crater, about 140 kilometers in diameter, about the size of the LA Basin, and in the middle of this crater we've got a mountain that goes up five kilometers high. So the peak of that mountain has more elevation on it than you've got in the lower 48 states here in the US. So it's even higher than Mount Whitney is above sea level. So we believe that there was water that once flowed into this crater and we see the geomorphologic evidence for it. And so we chose our landing ellipse, what you see there in blue to be located as close to the mountain as possible because we believe that the lower rocks in that mountain were formed in the presence of water, possibly where an ancient lake once formed. So that was kind of our hypothesis going into it, was to test these decades old ideas that water was not just on the surface of Mars, which is what Spirit and Opportunity showed. But we once had great rivers that flowed across the surface of Mars as well and maybe left a lake behind. So here we see what looks like erosion of the crater rim. So this is a topographic map. So the hotter colors indicate higher topography and there's a structure called peace vallis, which is a canyon that's cut into bedrock. And that canyon goes up to the peak of the crater rim and leads us to believe that water once was generated near the crater rim, almost certainly by meteoric precipitation. It's very hard for us to imagine that ground water was important here. Because the source of the water seems to originate from a high point, not the low point. And so the water flowed down hill, and just like that diffusion equation showed, you basically have the highest flux in the transport of, of the solid material. The erosion rates are going to be higher where the slope is steeper, and the water flows more vigorously, and therefore it exerts a bigger sheer stress. And it picks up pieces of rock, plucks them out, and then sends them down into something called an alluvial fan. Now this alluvial fan is not as spectacularly developed as Eberswalde Crater was. But we do believe that it con, constituted strong enough evidence to pick this landing site in this area. The cool thing about it was is that the landing ellipse was located downstream of the Alluvial Fan. So if that Alluvial Fan stopped at the edge of a lake, maybe, just maybe we would land very close to what might have been an ancient lake. And so the idea, as always, that water flows downhill. And if you go to the low point, that's where you want to be. So that's why we picked this landing ellipse, right between the crater rim and right next to Mount Sharp. Okay, so we landed and what you can see is Curiosity, there on the left, a white dot, because the top of the rover is painted white, so it has very high albedo. And in this false color image, you can see that we created a blast zone during descent, where all the dust was blown away. So what looks dark in that picture, is actually rock and soil that's fairly free of the dust component. Now [COUGH] we were supposed to be driving towards the mountain, but when we realized that we were just five football fields away from a white tone rock that has very interesting properties and including the possibility that there was water once there. We decided to drive in the opposite direction to go and explore it, and we're glad that we did because it, it turns out that we kind of hit pay dirt there. Now about halfway across that, that plain that looks brown colored in this image, we found rocks that indicated that the water was once flowing across the surface. And here's what we found. The rock on the left is from Mars. That's what Curiosity discovered. It's a kind of rock that a geologist calls a conglomerate. Which is a bunch of cemented pebbles that indicate that water once flowed across the surface. And as the pebbles and pieces of rock get transported ar, along, they sort of bounce into each other, knock off the corners and get rounded up. And so what you see in front of this rock are the pebbles that are weathering out of the rock and becoming pebbles again today. So, the one that's in a circle there indicates a, a sort of a nickel size fragment of rock that's all been smoothed up by flow of water probably about 3.8 billion years ago across the surface of Mars. Now, the picture on the right is a rock that's quite young, by planetary standards. It's only a million years old. And you can see the same kinds of particles in there, fragments of rock, that have all been rounded up, and had their edges knocked off by their interactions in an ancient stream. So this is a really easy way for us to then determine that water once flowed vigorously in a quite large, stream system. That was comparable to the kinds of, of streams that, that will flow on Earth and in dry, generally dry climates. So here is one of those places, and to be as conservative as possible, we've gone to Atacama Desert, which is the driest place on Earth. Water almost never flows here, but when it does, it does it very vigorously. Usually there's a, there's a storm up in the Andes Mountains. Water comes flowing down. It stays in its channel until it gets near the end. Then it floods out. And where the people are walking around, they're all, where the, the flow left the channel. And, and then immediately decelerated and left all the mud behind. But in the channel itself is where all the pebbles get transported. And you can see in there how some are angular. Those are probably harder kinds of rocks that derive from the source region up in the mountains. And then there's other rocks, they've been transported probably just as far, but they're softer rocks and they're rounder. Because they've been beat up more as they, as sort of the kinetics of the interaction of, of hitting each other as they move down the stream channel. Anyway, so this was Curiosity's first significant discovery that we were able to confirm something that had been seen all the way back in the sixties. That there really is evidence that rivers once flowed across the surface of Mars. The question then became could we kind of go with the flow and work our way downhill to where a lake may have been?

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